Federal regulations covering truck air brake systems require air flow capacity sufficient to pressurize the vehicle air brake chambers to 60 pounds per square inch (psi) within 0.30 second measured from the instant of brake actuation by a driver. Exhaustion of the chambers from 95 psi to 5 psi must occur within 0.60 second measured from the first movement of the vehicle brake control during brake release. While the vehicle manufacturer must consistently meet these requirements with a satisfactory combination of components, such as air control valves and connecting tubing, the air flow capacity of individual components must be known originally at the time of manufacture and will necessarily be re-examined by testing during actual service periods as normal maintenance procedure for maintaining vehicles on the highways. Air brake control valves that will be subject to periodic testing can be divided into three general types: mechanically actuated, pilot operated, and through valves. Examples of mechanically actuated valves include foot operated brake application valve, trailer hand control valve, dash mounted push-pull valves and others. Pilot operated valves, as used on vehicles, are normally actuated in response to pneumatic signals. It is essential that highly accurate test apparatus be used in determining the flow capacity, response time, and consistency from run to run of pilot operated valves. These valves must permit flow from zero to the high pressure very rapidly. In the testing of such valves, extremely accurate and consistent synchronization is needed in timing the operation of such valves from the initial application of pressure thereto. Through valves, such as quick release valves, require the same characteristics from the timing control valve used in a test set up as pilot operated valves, except that a relatively large volume of high pressure air must be instantly available. Thus, the timing control valve ordinarily mounted on a test stand must have a flow capacity in excess of that of any valve connected to it for testing, otherwise, accurate flow capacity data cannot be obtained for the valve under test.
It is an object of this invention to provide a valve that opens extremely rapidly, provides high flow capacity, and is useful in controlling an electrical circuit to determine the exact instant in which air flow from the valve begins. Another object is to use portions of a valve as conductors within an electrical circuit so that fluid movement through the valve can be accurately correlated with time. Another object is to construct the valves so that the elements are sealed at all times in closed position with such tightness as to be leak proof and to provide the positive contact necessary for conducting an electrical circuit through circuit interrupting elements.